Given that's an HSE, it's probably Bosch late 99' and later use all Bosch for FI etc.
It could be a number of things, buddy of mine has had their 00' for a number of years now. When the air bag system fails, sometimes it can do wierd stuff.
Includes failing deflated and limiting the Rover to 35mph.
The air bag systems are actually really good and simple systems. Air bags take minutes to replace and don't cost anymore than a shock does.
Just like anything, you keep up on it, it works well.